In situ combustion process



HYDROCARBONS OUT w UNBURNED RESERVOIR J. R. HURLEY IN SITU COMBUSTION PROCESS Filed June 23, 1958 I PRODUCER & WATER GAS OUT COB/ZONE Nov. 1, 1960 AIR & STEAM IN CLEAN SAND INVENTOR. JR HURLEY BY M1 ATTORNEYS O com-:0

-;CLEAN SAND F/G. Z

Patented Nov. 1, 1960 Line IN SITU COMBUSTION PROQESS James R. Hurley, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed June 23, 1958, Ser. No. 743,655

7 Claims. (Cl. 2623) This invention relates to a process for recovering components of a carbonaceous deposit by in situ combustion. A specific aspect of the process pertains to the conversion of coke, left in a carbonaceous stratum by inverse in situ combustion, into fuel gas.

In situ combustion in the recovery of hydrocarbons from underground strata containing carbonaceous material is becoming more prevalent in the petroleum industry. In this technique of production, combustion is initiated in the carbonaceous stratum and the resulting combustion zone is caused to move through the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and, in the case of inverse drive, upgrades a substantial proportion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a borehole therein, followed by injection of air through the ignition borehole in the stratum, constitutes a direct air drive process for effecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum frequently plugs in front of the combustion zone because a heavy viscous liquid bank of hydrocarbon collects in the stratum in advance of the combustion zone which prevents movement of air to the combustion process. To overcome this difficulty and to permit the continued progress of the combustion zone through the stratum, inverse air injection has been resorted to. By this technique, a combustion zone is established around an ignition borehole by any suitable means and air is fed thru the stratum to the combustion zone from one or more surrounding boreholes. Most of the techniques utilized are also applicable to the gasification of coal veins.

When a carbonaceous stratum is produced by inverse in situ combustion with the fire front moving thru the stratum countercurrently to the flow of air, a substantial carbonaceous or coke residue remains in the stratum after passage of the fire front therethru. This coke residue is hot because of the high temperature combustion wave passing thru during the recovery process at which time the temperature of the stratum reaches the range of about 1100 to 1700 F. Tests on tar sands indicate that the coke residue amounts to about 3 weight percent of the stratum. Hence, recovery of this valuable fuel in usable form is highly desirable. This invention is concerned with the recovery of this residual coke in the form of a combustible fuel gas.

Accordingly, it is an object of the invention to provide a process for the recovery of components of a carbonaceous deposit by in situ combustion. Another object is to provide a process for recovering fuel components from residual coke remaining in a carbonaceous stratum after passage therethru of an inverse burning wave or combustion front. A further object is to provide a process for converting residual coke left by an inverse in situ combustion process, conducted in a carbonaceous stratum, into fuel gas. Other objects of the invention will become apparent upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises contacting a hot stratum containing residual coke, after an inverse burning wave, with air and steam so as to form a fuel gas comprising producer gas and water gas and recovering the fuel gas from the stratum. In practicing the invention, air and steam either in admixture or in separate streams are injected into the hot coke-containing stratum behind an inverse burning combustion front whereby the air and steam produce valuable fuel gas by reaction with the coke and the produced fuel gas is recovered thru one or more production boreholes in the stratum. Ordinarily in field operation a carbonaceous stratum is produced by causing a fire front to pass by successive rings of wells (radial drive) or straight rows of wells (line drive). The Wells immediately behind the first front in the inverse air injection process are production Wells while those immediately ahead of the fire front are air injection wells. As the first crosses a row of wells, these wells are then used as production wells and the next row of wells in the path of the combustion front become air injection wells.

A more complete understanding of the invention may be had by reference to the accompanying schematic drawing of which Figure l is a sectional plan view thru a carbonaceous stratum, such as an oil said, showing an in-line arrangement of wells for effecting the invention and Figure 2 is a similar view showing a ring pattern of Wells for a radial drive process in accordance with the invention.

Referring to Figure 1 parallel lines of boreholes 10, 12, 14, 16 and 18 penetrate a carbonaceous stratum 20. At the stage of the process illustrated, an inverse combustion front 22 is moving from the line of wells 14 to the line of wells 16 and a gas reaction zone 24 is moving thru the stratum intermediate the line of wells 10 and the line of wells 12 toward the latter wells. The in situ commustion process was initiated around wells 10 in conventional manner and the resulting combustion front was caused to move thru the stratum toward wells 12 by injecting air or other combustion-supporting, oxygen-containing gas thru wells 12. When the combustion front arrived at wells 12, injection thru these wells was terminated and the air was then injected thru wells 14, wells 10 being shut-in temporarily while wells 12 became production wells. In the same manner, as the combustion front arrives at the vicinity of Wells 14, these wells become production wells with wells 16 becoming air injection wells. After the combustion front 22 passes line of wells 14 and production is shifted to these wells from wells 12, the production of fuel gas from the hot residual coke in the stratum intermediate the line of wells 10 and line of wells 12 is initiated by injecting air and steam either in admixture or alternately in slugs thru wells 10 with recovery of produced fuel gas thru wells 12. As the injected air and steam contact hot coke in the burned over stratum, water gas and producer gas are produced. These two gas reactions and their proper proportions are given below.

Water gas reaction: C+H O=CO+H Producer gas reaction: l.08C+.54O =l.03CO

If 4.32 pounds of air is injected per pound of steam enough heat is developed by burning the coke with oxygen to sustain the endothermic water gas reaction without reduction in stratum temperature. However, it is not essential to maintain the original stratum temperature in all cases and the amount of injected air may range from about 2 to 8 pounds per pound of steam. The heating value of the produced fuel gas is about 2200 B.t.u. per cubic foot. Since the amount of coke left in the stratum after the inverse burning wave is about 3 weight percent of the stratum, the fuel gas produced is sufiicient to operate engines and boilers to supply all required compressed air andsteam to the in situ combustion process as well as to the fuel gas process, itself.

As combustion front 22 moves beyond line of wells 16, fuel gas reaction zone 24 passes line of wells 12 so that wells 14 no longer serve as production Wells for the in situ combustion process, sustained by injecting air thru wells 18 and producing thru wells 16, and may now be utilized as fuel gas production wells while re-- action zone 24 is passing from wells 12 to wells 1.4.

While the operation has been described as utilizing Wells 10 as air and steam injection wells, it is also feasible to utilize wells 12 as air and steam injection wells with recovery of produced fuel gas thru wells 11} and shifting the air and steam injection to Wells 14 as reaction zone 24- reaches line of wells 10.

At the beginning of the fuel gas production step thru any line of wells, if the coke temperature in the stratum is lower than desired for efiicient water-gas reaction, the injection of air alone or in high ratio to steam such as 8 to 1 or even higher may be utilized for a short period, or as long as necessary, to reestablish a desired stratum temperature. Thermocouples in the production borehole can be utilized to determine approximate stratum temperature. The composition of the produced fuel gas is also an indication of the temperature being maintained in the reaction zone.

Referring to Figure 2, a central well 30 is surrounded by successive rings of wells 32, 34, and 36 in a carbonaceous stratum 26. Combustion zone 22 at the stage of the process illustrated is moving from ring of wells 34 to ring of wells 36 by injection of air thru wells 36 and produced hydrocarbons are being recovered thru wells 34. Fuel gas reaction zone 24 is moving outwardly from central well 30 to ring of wells 32, with air and steam injection thru well 33 and recovery of fuel gas thru ring of wells 32. The operation of the process illustrated with the well pattern of Figure 2 is very similar to that de scribed in connection with Figure 1. As combustion zone 22 reaches the outer ring of Wells 36, air injection thru another outer ring of wells (not shown) is initiated so as to continue the movement of the combustion front radially outwardly from central well 38. At this time, reaction zone 24 will have reached the first ring of wells 32 so that air and steam injection thru ring of wells 32 can be initiated so as to produce fuel gas from the hot coke between wells 32 and 34 and drive the same out thru wells 34.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. A process for producing a fuel gas which comprises injecting gas consisting essentially of air and steam in a ratio in the range of 2 to 8 pounds of air per pound of steam into a hot stratum containing about 3 weight percent residual coke at a temperature in the range of 1100 to 1700 F., left at this temperature by passing an inverse in situ combustion front thru said stratum, so as to react said gas with said coke to produce fuel gas comprising producer gas and water gas and recovering said fuel gas from said stratum.

2. The process of claim 1 wherein at least 4.32 pounds of air per pound of steam is injected to maintain the reaction at a temperature in said range.

3. The process of claim 1 wherein said combustion front is moved thru said stratum from a first well to a second well by injecting air thru said second well; when said front reaches said second well, same is moved thru said stratum to a third well by injecting air thru said third well and producing thru said second well; when said front reaches said third well, same is moved thru said stratum to a fourth wellby injecting air thru said fourth Well and producing thru said third well; and, while said front is being moved from said third well to said fourth well, injecting air and steam into the hot coke in said stratum intermediate said first and second wells so as to produce fuel gas.

4. The process of claim 3 wherein said air andsteam are injected thru said first well and said fuel gas is recovered thru said second well.

5. The process of claim 3 wherein said first, second, third, and fourth wells are in 4 separate parallel lines of in-line Wells, and injection into and recovery from the several wells in each line is practiced as for the'numbered wells.

6. The process of claim 3 wherein said first well is a central well and said second, third, and fourth wells are in separate rings of wells around said first well, andinjection into and recovery from the several wells in each ring is practiced as for the numbered wells.

7. A process comprising moving a combustion front thru a carbonaceous oil-containing stratum from a first Well to a second Well therein by igniting said stratum around said first well and injecting air thru said second well; when said front reaches said second well, moving same thru said stratum to a third well by injecting air thru said third well and producing hydrocarbon thru said second well; when said front reaches said third well, moving same thru said stratum to a fourth well by'injecting air thru said fourth well and producing hydrocarbons thru said third well; while said front is being moved from said third well to said fourth well, injecting gas consisting essentially of air and steam into the hot coke in said stratum intermediate said first and second wells so as to convert said coke and gas to fuel gas; and recovering said fuel gas. 7

References Cited in the file of this patent UNITED STATES PATENTS 1,913,395 Karrick June 13, 1933 1,919,636 Karriclt July 25, 1933 2,642,943 Smith June 23, 1953 2,695,163 Pearce etal Nov. 23, 1954 2,786,660 Alleman far. 26, 1957 2,793,696 Morse May 28, 1957 2,818,118 Dixon Dec. 31, 1957 2,841,375 Salomonsson July 1, 1958 2,889,881 Trantham et al. June 9, 1959 

